Method of providing high coefficients of friction across oil-lubricating friction clutches

ABSTRACT

The invention concerns a method of increasing the dynamic coefficient of friction in an oil-lubricated friction clutch by using a lubricating oil containing at least one specific copolymer, the presence of which develops higher dynamic friction levels in the clutch.

This invention relates to a method of increasing the dynamic coefficient of friction in an oil-lubricated friction clutch, so providing a friction clutch-lubricant system capable of providing high levels of torque transfer in applications such as vehicular automatic transmissions. More particularly, the present invention is directed to a method of increasing the friction in an oil-lubricated friction clutch using a lubricating oil containing at least one copolymer as hereinafter defined, the presence of which develops higher dynamic friction levels in oil-lubricated clutches than otherwise comparable lubricants formulated without the specified copolymer.

BACKGROUND OF THE INVENTION

The continuing pursuit of more fuel efficient motor vehicles is forcing vehicular automatic transmission builders to make transmissions ever more energy efficient. There are a number of types of automatic transmission including stepped automatic transmissions, automated manual transmissions, continuously variable transmissions and dual clutch transmissions. Each type of automatic transmission offers its own advantages over the others when used in motor vehicles, however, the ability to reduce size and weight provides a benefit regardless of type, particularly in the pursuit of increased fuel efficiency. In any automatic transmission where a paper composite, oil-lubricated clutch is used (e.g. stepped automatic transmissions, continuously variable transmissions and dual clutch transmissions), reduction in the size of the transmission by, for example, reducing the number of plates used in the clutch will reduce the size and weight of the overall transmission. Increasing the friction level in the clutch has the desirable effect of increasing the level of torque that can be transferred through the clutch which, in turn, requires less surface area to transmit the same amount of torque. Therefore, in an oil-lubricated clutch having, for example, five fiber plates, a 20% increase in dynamic friction provided by the lubricant would allow for the removal of one paper plate and one steel plate, thereby providing a corresponding 20% decrease in the weight and size of the clutch. Such hardware reductions assist a vehicle manufacturer to design lighter vehicles with attendant fuel efficiency benefits, as well as reducing the complexity of component design, with attendant cost and reliability benefits.

In non-automotive applications increasing the dynamic coefficient of friction is also a desirable attribute, because it improves the controllability and overall operation of the clutch.

There remains in the art a continuing need for improved means to provide high dynamic friction within power transmission devices, to enable high torque transfer. Such means assist the vehicle designer to meet the modern demands for fuel-efficient, reliable, low-maintenance transmissions with good driveability.

Applicants have now discovered that lubricating oils, particularly lubricating power transmitting oils, more particularly automatic transmission oils, incorporating certain copolymers as hereinafter defined, when used in conjunction with oil-lubricated friction clutches having composite (i.e. cellulose-based) friction linings, deliver increased levels of dynamic friction that enable the transmissions in which they are used to be made smaller, decreasing the size and weight of the transmission and resulting in an improvement in fuel efficiency and hardware design considerations for the overall vehicle. These dynamic friction increasing polymers function in the lubricating oil alone, and also in a preferred embodiment when used in combination with performance enhancing additive packages.

In a preferred embodiment of the present invention, Applicants have discovered that the polymers described hereinunder are particularly effective in co-operation with ashless dispersants to increase the dynamic coefficient of friction of a lubricant for oil-lubricated friction clutches.

In a further preferred embodiment of the present invention, Applicants have discovered that the polymers described hereinunder are particularly effective in co-operation with additive performance packages to increase the dynamic coefficient of friction of a lubricant for oil-lubricated friction clutches.

Copolymers of (meth)acrylic esters, be they non-functionalised or even functionalised by introducing amine functionalities via N,N-dimethylaminopropyl methacrylamide DMAPMAAm are known in the industry; see for example R. M. Mortier, S. T. Orszulik (eds.), Chemistry and Technology of Lubricants, Blackie Academic & Professional, London 1993.

US-A-2008/0146475 to Mueller, Stoehr and Eisenberg (Rohmax Additives GmbH) discloses various copolymers of (meth)acrylic esters involving N/O-functional monomers such as the N-(2-methacryloyl oxylethyl)ethylene urea (short name “ethylene urea methacrylate” EUMA). The polymers are disclosed in the context of friction reducing additives for oils. All the worked examples of this invention relate to block copolymers, and whilst this document mentions the possibility of random copolymers, it does not contemplate the structure of the polymer being critical to performance in the oil.

EP-A-0 339 088 and U.S. Pat. No. 3,925,217 describe the use of polymers or compounds with cyclic substituents as means to achieve high friction coefficients. They do not contemplate the polymers hereinafter described.

SUMMARY OF THE INVENTION

In a first aspect, the present invention is a method of increasing the friction in an oil-lubricated friction clutch having a cellulose-based friction lining, or in a power-transmission device utilising said clutch, the method comprising:

-   -   (i) preparing or otherwise obtaining a lubricant composition         comprising         -   (i.a) a major amount of oil of lubricating viscosity, and         -   (i.b) one or more copolymers of ethylenically unsaturated             esters present in an amount effective to increase the             dynamic coefficient of friction of the lubricant composition             when used in said clutch or device; and     -   (ii) lubricating said clutch or device with the lubricant         composition resulting from step (i);         wherein at least one copolymer (i.b) is a statistical copolymer         derived essentially from the following monomers (a) and (b):         (a) at least one ethylenically unsaturated ester compound of the         formula (I)

in which R is hydrogen or methyl, R¹ is a linear or branched chain alkyl group having from 6 to 36 carbon atoms, and R² and R³ are each independently hydrogen or a group of the formula —COOR′ in which R′ is hydrogen or a linear or branched chain alkyl group having from 6 to 36 carbon atoms; and (b) at least one ethylenically unsaturated ester compound of the formula (II)

in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula —NH— or —NR^(a)— in which R^(a) is an alkyl radical having from 1 to 40 carbon atoms, R⁴ is a radical comprising from 2 to 100 carbon atoms and contains at least 2 oxygen, sulfur or nitrogen atoms, R⁵ and R⁶ are each independently hydrogen or a group of the formula —COX′R⁷ in which X′ is oxygen or an amino group of the formula —NH— or —NR^(a′)— in which R^(a′) is an alkyl radical having from 1 to 40 carbon atoms, and R⁷ is a radical comprising from 1 to 100 carbon atoms; wherein the monomer units originating from monomer (b) constitute from 0.1 to 30 weight percent of the total weight of said statistical copolymer.

Applicants have surprisingly found that the statistical copolymers defined in the above method increase the dynamic coefficients of friction of lubricant compositions for oil-lubricated friction clutches. In particular, the polymer architecture resulting from the statistical monomer distribution, in combination with the nature and relative proportion of units derived from the monomer (b), provides excellent dynamic friction-increasing properties for lubricating oils.

In this respect, Applicants have particularly found that the dynamic coefficient of friction is especially increased where the level of monomer (b) is below 10 weight percent of the total weight of such statistical copolymer, more preferably in the range of 1 to 6 weight percent; and more preferably where the weight-average molecular weight, Mw, as measured by GPC, is also within the range of 10,000 to 60,000, and most preferably within the range of 40,000 to 60,000 g/mol, as determined, for example, in tetrahydrofuran at 35° C. against a polymethyl methacrylate calibration curve composed of a set of at least 25 standards (obtainable from the Polymer Standards Service or Polymer Laboratories, Mainz, Germany) whose M_(peak) is distributed in logarithmically uniform manner over the range from 5·10⁶ to 2·10² g/mol. For this purpose it is possible to use combinations of six GPC columns (for example: Polymer Standards Service SDV 100 Å/2x SDV LXL/2x S SDV 100 Å/Shodex KF-800D) as is known in the art.

In a preferred embodiment of the first aspect of the invention, the lubricant composition resulting from step (i) additionally comprises (i.c) an ashless dispersant, wherein said dispersant is present in an amount that is effective in combination with the copolymer (i.b) to increase the dynamic coefficient of friction of the lubricant composition when used in said clutch or device.

In this preferred embodiment, Applicants have particularly found that the level of dynamic friction of the lubricant is especially increased where the level of monomer (b) is below 10 weight percent of the total weight of said statistical copolymer, more preferably in the range of 6 to 10 weight percent; and more preferably where the weight-average molecular weight, Mw, as measured by GPC, is also within the range of 10,000 to 60,000, and most preferably within the range of 10,000 to 40,000 g/mol as measured against the above-referenced standards.

In a second aspect, the invention is the use of one or more statistical copolymers derived essentially from the following monomers (a) and (b):

-   -   (a) at least one ethylenically unsaturated ester compound of the         formula (I)

-   -   in which R is hydrogen or methyl, R¹ is a linear or branched         chain alkyl group having from 6 to 36 carbon atoms, and R² and         R³ are each independently hydrogen or a group of the formula         —COOR′ in which R′ is hydrogen or a linear or branched chain         alkyl group having from 6 to 36 carbon atoms; and     -   (b) at least one ethylenically unsaturated ester compound of the         formula (II)

-   -   in which R is hydrogen or methyl, X is oxygen, sulfur or an         amino group of the formula —NH— or —NR^(a)— in which R^(a) is an         alkyl radical having from 1 to 40 carbon atoms, R⁴ is a radical         comprising from 2 to 100 carbon atoms and contains at least 2         oxygen, sulfur or nitrogen atoms, R⁵ and R⁶ are each         independently hydrogen or a group of the formula —COX′R⁷ in         which X′ is oxygen or an amino group of the formula —NH— or         —NR^(a′)— in which R^(a′) is an alkyl radical having from 1 to         40 carbon atoms, and R⁷ is a radical comprising from 1 to 100         carbon atoms;         wherein the monomer units originating from monomer (b)         constitute from 0.1 to 30 weight percent of the total weight of         said statistical copolymer;         in a lubricant composition comprising a major amount of oil of         lubricating viscosity, to increase the dynamic coefficient of         friction exhibited by the lubricant composition in an         oil-lubricated friction clutch having a cellulose-based friction         lining or in a power-transmission device utilising said clutch.

In a third aspect, the invention is the use of an ashless dispersant in co-operation with one or more statistical copolymers derived essentially from the following monomers (a) and (b):

-   -   (a) at least one ethylenically unsaturated ester compound of the         formula (I)

-   -   in which R is hydrogen or methyl, R¹ is a linear or branched         chain alkyl group having from 6 to 36 carbon atoms, and R² and         R³ are each independently hydrogen or a group of the formula         —COOR′ in which R′ is hydrogen or a linear or branched chain         alkyl group having from 6 to 36 carbon atoms; and     -   (b) at least one ethylenically unsaturated ester compound of the         formula (IV)

-   -   in which R is hydrogen or methyl, X is oxygen, sulfur or an         amino group of the formula —NH— or —NR^(a)— in which R^(a) is an         alkyl radical having from 1 to 40 carbon atoms, R⁴ is a radical         comprising from 2 to 100 carbon atoms and contains at least 2         oxygen, sulfur or nitrogen atoms, R⁵ and R⁶ are each         independently hydrogen or a group of the formula —COX′R⁷ in         which X′ is oxygen or an amino group of the formula —NH— or         —NR^(a′)— in which R^(a′) is an alkyl radical having from 1 to         40 carbon atoms, and R⁷ is a radical comprising from 1 to 100         carbon atoms;         wherein the monomer units originating from monomer (b)         constitute from 0.1 to 30 weight percent of the total weight of         said statistical copolymer;         in a lubricant composition comprising a major amount of oil of         lubricating viscosity, to increase the dynamic coefficient of         friction exhibited by the lubricant composition in an         oil-lubricated friction clutch having a cellulose-based friction         lining or in a power-transmission device utilising said clutch.

In this third aspect of the invention, the combined presence of dispersant and the defined statistical copolymer(s) surprisingly brings about an increase in dynamic coefficient of friction in the clutch or device, particularly at higher operational speeds, that is greater than the increase observed for the corresponding copolymer(s) alone.

In a fourth aspect, the invention is the use of one or more statistical copolymers (as defined under the above method or use aspects of the invention) in combination with one or more additive performance packages, to increase the dynamic coefficient of friction exhibited by the lubricant composition in an oil-lubricated friction clutch having a cellulose-based friction lining or in a power-transmission device utilising said clutch.

In this fourth aspect of the invention, the combined presence of additive performance package and the defined statistical copolymer(s) surprisingly brings about an increase in dynamic coefficient of friction in the clutch or device that is greater than the increase observed for the corresponding copolymer(s) alone.

Other aspects of the invention, along with preferred embodiments for all aspects, are disclosed hereafter in the description and in the dependent claims.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 and 2 show graphically the relationship between friction coefficient and sliding speed achieved using the lubricating oil compositions of Performance Example 2.

FIGS. 3 and 4 show graphically the relationship between friction coefficient and sliding speed achieved using the lubricating oil compositions of Performance Example 3.

DETAILED DESCRIPTION OF THE INVENTION

The ability to provide high levels of dynamic friction in oil lubricated clutches with cellulose-based (for example, paper composite) friction linings is a highly desirable property of a clutch lubricant, for the reasons stated above. The increase in dynamic friction levels over those provided by conventional lubricants can be accomplished by the use of the above defined statistical copolymers.

The necessary components of all aspects of the invention are described below in more detail.

Component i.a.

Oils of lubricating viscosity useful in the practice of the present invention are natural lubricating oils, synthetic lubricating oils and mixtures thereof. Suitable lubricating oils also include base stocks obtained by isomerization of synthetic wax and slack wax, as well as base stocks produced by hydrocracking (rather than by solvent treatment) the aromatic and polar components of a crude oil. In general, suitable lubricating oils will have a kinematic viscosity ranging from about 1 to about 40 mm²/s (cSt) at 100° C. Typical applications will require the lubricating oil base stocks or base stock mixture to have a viscosity preferably ranging from about 1 to about 40 mm²/s (cSt), more preferably, from about 2 to about 8 mm²/s (cSt), most preferably, from about 2 to about 6 mm²/s (cSt), at 100° C.

Natural lubricating oils include animal oils, vegetable oils (e.g., castor oil and lard oil), petroleum oils, mineral oils, and oils derived from coal or shale. The preferred natural lubricating oil is mineral oil.

The mineral oils useful in the practice of the invention include all common mineral oil base stocks. This would include oils that are naphthenic or paraffinic in chemical structure as well as oils that are refined by conventional methodology using acid, alkali, and clay or other agents such as aluminum chloride, as well as extracted oils produced, e.g., by solvent extraction or treatment with solvents such as phenol, sulfur dioxide, furfural, dichlorodiethyl ether, etc. They may be hydro treated or hydro refined, dewaxed by chilling or catalytic dewaxing processes, or hydro cracked. The mineral oil may be produced from natural crude sources or be composed of isomerized wax materials or residues of other refining processes.

A particularly useful class of mineral oils includes those mineral oils that are severely hydro treated or hydro cracked. These processes expose the mineral oils to very high hydrogen pressures at elevated temperatures in the presence of hydrogenation catalysts. Typical processing conditions include hydrogen pressures of approximately 3000 pounds per square inch (psi) at temperatures ranging from 300° C. to 450° C., over a hydrogenation-type catalyst. This processing removes sulfur and nitrogen from the lubricating oil and saturates any alkylene or aromatic structures in the feedstock. The result is a base oil with extremely good oxidation resistance and viscosity index. A secondary benefit of these processes is that low molecular weight constituents of the feed stock, such as waxes, can be isomerized from linear to branched structures thereby providing finished base oils with significantly improved low temperature properties. These hydro treated base oils may then be further de-waxed either catalytically or by conventional means to give them exceptional low temperature fluidity. Commercial examples of lubricating base oils made by one or more of the aforementioned processes are Chevron RLOP, Petro-Canada P65, Petro-Canada P100, Yukong, Ltd., Yubase 4, Imperial Oil Canada MXT, and Shell XHVI 5.2. These materials are commonly referred to as API Group III mineral oils.

Typically such mineral oils will have kinematic viscosities of from about 1.0 mm²/s (cSt) to about 40.0 mm²/s (cSt) at 100° C. Preferred mineral oils have kinematic viscosities of from about 2 to about 8 mm²/s (cSt), and most preferred are those mineral oils with kinematic viscosities of from about 2 to about 6 mm²/s (cSt), at 100° C.

Synthetic lubricating oils useful in the practice of the invention include hydrocarbon oils and halo-substituted hydrocarbon oils such as oligomerized, polymerized, and interpolymerized olefins (e.g., polybutylenes, polypropylenes, propylene, isobutylene copolymers, chlorinated polylactenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes), etc., and mixtures thereof); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzene, etc.); polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.]; and alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as derivatives, analogs, and homologs thereof, and the like. The preferred oils from this class of synthetic oils are oligomers of α-olefins, particularly oligomers of 1-decene. These materials are commonly referred to as poly-α-olefins.

Synthetic lubricating oils also include alkylene oxide polymers, interpolymers, copolymers, and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc. This class of synthetic oils is exemplified by: polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide; the alkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having an average molecular weight of 1000, diphenyl ether of polypropylene glycol having a molecular weight of 1000-1500); and mono- and poly-carboxylic esters thereof (e.g., the acetic acid esters, mixed C₃-C₈ fatty acid esters, and C₁₂ oxo acid diester of tetraethylene glycol).

Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids, alkenyl malonic acids, etc.) with a variety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycol monoethers, propylene glycol, etc.). Specific examples of these esters include dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the complex ester formed by reacting one mole of sebasic acid with two moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid, and the like. Preferred types of synthetic oils include adipates of C₄ to C₁₂ alcohols.

Esters useful as synthetic lubricating oils also include those made from C₅ to C₁₂ monocarboxylic acids and polyols and polyol ethers such as neopentyl glycol, trimethylolpropane pentaerythritol, dipentaerythritol, tripentaerythritol, and the like.

Silicon-based oils (such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils) comprise another useful class of synthetic lubricating oils. These oils include tetraethyl silicate, tetraisopropyl silicate, tetra(2-ethylhexyl) silicate, tetra(4-methyl-2-ethylhexyl) silicate, tetra(p-tert-butylphenyl) silicate, hexa(4-methyl-2-pentoxy)disiloxane, poly(methyl) siloxanes and poly(methylphenyl) siloxanes, and the like. Other synthetic lubricating oils include liquid esters of phosphorus-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, and diethyl ester of decylphosphonic acid), polymeric tetra-hydrofurans, poly-α-olefins, and the like.

The lubricating oils may be derived from refined oils, re-refined oils, or mixtures thereof. Unrefined oils are obtained directly from a natural source or synthetic source (e.g., coal, shale, or tar sands bitumen) without further purification or treatment. Examples of unrefined oils include a shale oil obtained directly from a retorting operation, petroleum oil obtained directly from distillation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Refined oils are similar to the unrefined oils except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques include distillation, hydrotreating, dewaxing, solvent extraction, acid or base extraction, filtration, and percolation, all of which are known to those skilled in the art. Re-refined oils are obtained by treating used oils in processes similar to those used to obtain the refined oils. These re-refined oils are also known as reclaimed or reprocessed oils and are often additionally processed for removal of spent additives and oil breakdown products.

In particular cases, synthetic base oils originating from gas-to-liquid (GTL), coal-to-liquid (CTL) or biomass-to-liquid (BTL) processes can be applied. Their higher raw material costs compared to mineral oils may be compensated for by advantageous properties and performance.

Typically, the lubricating oil used in this invention will be a natural lubricating oil. If a synthetic lubricating oil basestock is used, it is preferably a poly-α-olefin, monoester, diester, polyester, or mixtures thereof. The preferred synthetic lubricating oil is a poly-α-olefin.

Component i.b.

Component i.b. is at least one statistical copolymer derived essentially from the following monomers (a) and (b):

-   -   (a) at least one ethylenically unsaturated ester compound of the         formula (I)

-   -   in which R is hydrogen or methyl, R¹ is a linear or branched         chain alkyl group having from 6 to 36 carbon atoms, preferably         from 6 to 24 carbon atoms and more preferably from 6 to 15         carbon atoms; and R² and R³ are each independently hydrogen or a         group of the formula —COOR′ in which R′ is hydrogen or a linear         or branched chain alkyl group having from 6 to 36 carbon atoms,         preferably from 6 to 24 carbon atoms and more preferably from 6         to 15 carbon atoms; and     -   (b) at least one ethylenically unsaturated ester compound of the         formula (II)

-   -   in which R is hydrogen or methyl, X is oxygen, sulfur or an         amino group of the formula —NH— or —NR^(a)— in which R^(a) is an         alkyl radical having from 1 to 40 carbon atoms, R⁴ is a radical         comprising from 2 to 100 and preferably 2 to 20 carbon atoms and         contains at least 2 oxygen, sulfur or nitrogen atoms, R⁵ and R⁶         are each independently hydrogen or a group of the formula         —COX′R⁷ in which X′ is oxygen or an amino group of the formula         —NH— or —NR^(a′)— in which R^(a′) is an alkyl radical having         from 1 to 40 carbon atoms, and R⁷ is a radical comprising from 1         to 100 carbon atoms;         wherein the monomer units originating from monomer (b)         constitute from 0.1 to 30         weight percent of the total weight of said statistical         copolymer.

In this specification, the term of art “statistical” is used to denote a copolymer that is derived from direct copolymerization of a mixture of two (or more) co-monomers under reaction conditions where the next co-monomer to insert into a growing polymer chain follows from the statistical distribution of co-monomers in the monomer mixture. In such copolymers the co-monomer units are interspersed throughout the backbone, rather than present in discrete homopolymeric blocks.

As the skilled person knows, in the direct polymerization of two or more co-monomers, the order of addition of the co-monomers into growing copolymer chains is determined in particular by the relative reactivities of the co-monomers, and the relative proportions of the co-monomers in the monomer mixture. The co-monomers (a) and (b) (and any additional co-monomers) used to derive the copolymers of the present invention have similar reactivities, meaning that the reactivity of co-monomer (a) towards another co-monomer (a) is similar to its reactivity towards co-monomer (b). In such copolymers, different co-monomer units are interspersed throughout the backbone, in an order largely governed by their distribution in the monomer mixture as the copolymerisation evolved, typically following a statistical rule such as Bernoullian statistics or Markovian statistics. Such polymers differ fundamentally from highly-ordered polymers such as block copolymers (essentially derived from successive homopolymerisations of sequentially-added monomers) and alternating copolymers (essentially derived from co-monomers with selective reactivities, that lead to a highly ordered ‘-A-B-A-B-A-B-’ type arrangement of units in the polymer chain).

A statistical copolymer wherein the probability of finding a particular type of co-monomer unit at any particular point in the polymer chain is independent of the type(s) of surrounding co-monomer (i.e. where co-monomer reactivities are equivalent) can be referred to as a truly “random” copolymer. Such copolymers fall within the meaning of “statistical” as used herein, and represent the outcome of polymer chain growth that is controlled solely by the distribution of co-monomers in the monomer mixture.

In accordance with the invention, Applicants have found that the combination of the defined co-monomers and a statistical copolymer architecture with a relatively low content of monomer units derived from co-monomer (b), results in a copolymer which, when added to a lubricating oil, functions to increase the dynamic coefficient of friction of the oil when used to lubricate friction clutches or devices utilizing them. The use of such copolymers as additives for such oils thereby enables the reductions in hardware and attendant benefits described above.

In a preferred embodiment of all aspects of the invention, the inclusion in the copolymer chains of units derived from additional co-monomers conveys on the copolymer further advantageous performance, leading to copolymers that are multi-functional in their additive performance.

Preferably the statistical copolymer defined under all aspects of the invention is essentially derived from a mixture of co-monomers (a), (b) and one or more additional monomers of the type (c) as hereinafter described. The additional interspersion of co-monomer (c) into the backbone causes the resulting copolymer to function both to increase dynamic friction in the above described oil-lubricated friction clutches (or power-transmission devices containing them) and to favourably modify the temperature-dependent viscosity characteristics of the lubricant composition, providing a combination of advantages to the lubricant.

The co-monomers suitably employed in the working of all aspects of the invention are hereafter described in more detail.

Monomer (a) is one or more ethylenically unsaturated ester compounds of the formula

in which R is hydrogen or methyl, R′ is a linear or branched alkyl radical having from 6 to 36 carbon atoms and preferably from 6 to 24 carbon atoms, more preferably 6 to 15 carbon atoms, R² and R³ are each independently hydrogen or a group of the formula —COOR′ in which R′ is hydrogen or an alkyl group having from 6 to 36 atoms and preferably from 6 to 24 carbon atoms, more preferably 6 to 15 carbon atoms.

Preferred embodiments of monomer (a) are acrylates, methacrylates and mixtures thereof (hereinafter collectively termed “(meth)acrylates”), fumarates and maleates, all of which are derived from alcohols of the formula R¹OH. More preferably monomer (a) is one or more acrylates or methacrylates, or mixtures thereof derived from alcohols of the formula R¹OH.

Monomer (a) may be one or more (meth)acrylates which derive from unsaturated alcohols, for example oleyl (meth)acrylate; cycloalkyl (meth)acrylates such as 3-vinylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, bornyl (meth)acrylate; and also the corresponding fumarates and maleates.

More preferably, monomer (a) is one or more compounds selected from the group consisting of hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, 2-tert-butylheptyl (meth)acrylate, octyl (meth)acrylate, 3-isopropylheptyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate, dodecyl (meth)acrylate, 2-methyldodecyl (meth)acrylate, tridecyl (meth)acrylate, 5-methyltridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate.

Most preferably, monomer (a) is an acrylate or methacrylate (or mixture thereof) wherein, in formula (I), R¹ is a linear or branched alkyl radical having from 12 to 15 carbon atoms, R is methyl and R² and R³ are each preferably hydrogen.

Monomer (b) is at least one ethylenically unsaturated ester compound of the formula:

in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula —NH— or —NR^(a)— in which R^(a) is an alkyl radical having from 1 to 40 carbon atoms, R⁴ is a radical comprising from 2 to 100 carbon atoms, preferably 2 to 20 carbon atoms, and contains at least 2 oxygen, sulfur or nitrogen atoms, R⁵ and R⁶ are each independently hydrogen or a group of the formula —COX′R⁷ in which X′ is oxygen or an amino group of the formula —NH— or —NR^(a′)— in which R^(a′) is an alkyl radical having from 1 to 40 carbon atoms, and R⁷ is a radical comprising from 1 to 100 carbon atoms.

In formula (II), X is oxygen, sulfur or an amino group of the formula —NH— or —NR^(a)— in which R^(a) is an alkyl radical having from 1 to 40, preferably from 1 to 4 carbon atoms.

Preferably, the R⁴ radical in the monomer units originating from at least one monomer (b) comprises at least one nitrogen atom and at least one oxygen atom.

More preferably, the R⁴ radical in the monomer units originating from at least one monomer (b) comprises at least one urea group.

The R⁵ and R⁶ radicals in formula (II) are each independently hydrogen or a group of the formula —COX′R⁷ in which X′ is oxygen, sulfur or an amino group of the formula —NH— or —NR^(a′)— in which R^(a′) is an alkyl radical having from 1 to 40 carbon atoms, preferably from 1 to 4 carbon atoms, and R⁷ is a radical comprising from 1 to 100, preferably from 1 to 30 and more preferably from 1 to 15 carbon atoms. The expression “radical comprising from 1 to 100 carbon atoms” indicates radicals of organic compounds having from 1 to 100 carbon atoms. It encompasses aromatic and heteroaromatic groups, and also alkyl, cycloalkyl, alkoxy, cycloalkoxy, alkenyl, alkanoyl, alkoxycarbonyl groups and heteroaliphatic groups. The groups mentioned may be branched or unbranched.

The R⁴ radical is a radical comprising from 2 to 100, preferably from 2 to 20 carbon atoms. The expression “radical comprising from 2 to 100 carbon atoms” indicates radicals of organic compounds having from 2 to 100 carbon atoms. It includes aromatic and heteroaromatic groups, and alkyl, cycloalkyl, alkoxy, cycloalkoxy, alkenyl, alkanoyl, alkoxycarbonyl groups, and also heteroaliphatic groups. The groups mentioned may be branched or unbranched. In addition, these groups may have customary substituents. Substituents are, for example, linear and branched alkyl groups having from 1 to 6 carbon atoms, for example methyl, ethyl, propyl, butyl, pentyl, 2-methylbutyl or hexyl; cycloalkyl groups, for example cyclopentyl and cyclohexyl; aromatic groups such as phenyl or naphthyl; amino groups, ether groups, ester groups and halides.

According to the invention, aromatic groups denote radicals of mono- or polycyclic aromatic compounds having preferably from 6 to 20, in particular from 6 to 12, carbon atoms. Heteroaromatic groups denote aryl radicals in which at least one CH group has been replaced by N and/or at least two adjacent CH groups have been replaced by S, NH or O, heteroaromatic groups having from 3 to 19 carbon atoms.

Aromatic or heteroaromatic groups preferred in accordance with the invention derive from benzene, naphthalene, biphenyl, diphenyl ether, diphenylmethane, diphenyldimethylmethane, bisphenone, diphenyl sulfone, thiophene, furan, pyrrole, thiazole, oxazole, imidazole, isothiazole, isoxazole, pyrazole, 1,3,4-oxadiazole, 2,5-diphenyl-1,3,4-oxadiazole, 1,3,4-thiadiazole, 1,3,4-triazole, 2,5-diphenyl-1,3,4-triazole, 1,2,5-triphenyl-1,3,4-triazole, 1,2,4-oxadiazole, 1,2,4-thiadiazole, 1,2,4-triazole, 1,2,3-triazole, 1,2,3,4-tetrazole, benzo[b]thiophene, benzo[b]furan, indole, benzo[c]thiophene, benzo[c]furan, isoindole, benzoxazole, benzothiazole, benzimidazole, benzisoxazole, benzisothiazole, benzopyrazole, benzothiadiazole, benzotriazole, dibenzofuran, dibenzothiophene, carbazole, pyridine, bipyridine, pyrazine, pyrazole, pyrimidine, pyridazine, 1,3,5-triazine, 1,2,4-triazine, 1,2,4,5-triazine, tetrazine, quinoline, isoquinoline, quinoxaline, quinazoline, cinnoline, 1,8-naphthyridine, 1,5-naphthyridine, 1,6-naphthyridine, 1,7-naphthyridine, phthalazine, pyridopyrimidine, purine, pteridine or quinolizine, 4H-quinolizine, diphenyl ether, anthracene, benzopyrrole, benzooxathiadiazole, benzooxadiazole, benzopyridine, benzopyrazine, benzopyrazidine, benzopyrimidine, benzotriazine, indolizine, pyridopyridine, imidazopyrimidine, pyrazinopyrimidine, carbazole, aciridine, phenazine, benzoquinoline, phenoxazine, phenothiazine, acridizine, benzopteridine, phenanthroline and phenanthrene, each of which may also optionally be substituted.

The preferred alkyl groups include the methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, 2-methylpropyl, tert-butyl radical, pentyl, 2-methylbutyl, 1,1-dimethylpropyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, nonyl, 1-decyl, 2-decyl, undecyl, dodecyl, pentadecyl and the eicosyl group.

The preferred cycloalkyl groups include the cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and the cyclooctyl group, each of which is optionally substituted with branched or unbranched alkyl groups.

The preferred alkenyl groups include the vinyl, allyl, 2-methyl-2-propenyl, 2-butenyl, 2-pentenyl, 2-decenyl and the 2-eicosenyl group.

The preferred alkynyl groups include the ethynyl, propargyl, 2-methyl-2-propynyl, 2-butynyl, 2-pentynyl and the 2-decynyl group.

The preferred alkanoyl groups include the formyl, acetyl, propionyl, 2-methylpropionyl, butyryl, valeroyl, pivaloyl, hexanoyl, decanoyl and the dodecanoyl group.

The preferred alkoxycarbonyl groups include the methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, tert-butoxycarbonyl, hexyloxycarbonyl, 2-methylhexyloxycarbonyl, decyloxycarbonyl or dodecyl-oxycarbonyl group.

The preferred alkoxy groups include alkoxy groups whose hydrocarbon radical is one of the aforementioned preferred alkyl groups.

The preferred cycloalkoxy groups include cycloalkoxy groups whose hydrocarbon radical is one of the aforementioned preferred cycloalkyl groups.

The preferred heteroatoms which are present in the R⁴ radical include oxygen, nitrogen, sulfur, boron, silicon and phosphorus, preference being given to oxygen and nitrogen.

The R⁴ radical comprises at least two, preferably at least three, heteroatoms.

The R⁴ radical in ester compounds of the formula (II) preferably has at least 2 different heteroatoms. In this case, the R⁴ radical in at least one of the ester compounds of the formula (II) may comprise at least one nitrogen atom and at least one oxygen atom.

In a particular aspect of the present invention, at least one heteroatom in the R⁴ radical in at least one of the ester compounds of the formula (II) may be separated from the X group by at least 4 atoms, more preferably by at least 6 atoms.

In a further aspect of the present invention, the R⁴ radical in at least one of the ester compounds of the formula (II) may comprise at least one group of the formula —CO— and at least one nitrogen atom.

In this case, the R⁴ radical in at least one of the ester compounds of the formula (II) may have at least one urea group, urea groups generally being representable by the formula —NR^(b)—CO—NR^(c)— in which the R^(b) and R^(c) radicals are each independently hydrogen or a group having from 1 to 40 carbon atoms, preferably from 1 to 20 carbon atoms and more preferably from 1 to 4 carbon atoms, or the radicals R^(b) and R^(c) radicals may form a ring having from 1 to 80 carbon atoms.

The R⁴ radical in at least one ester compound of the formula (II) is most preferably of a group of the formula (III):

in which A is a connecting group having from 1 to 500 carbon atoms, preferably from 1 to 50 carbon atoms, and more preferably from 1 to 10 carbon atoms. The expression “connecting group having from 1 to 500 carbon atoms” has already been explained in detail above.

More preferably, in the formula (III), A is an alkoxyalkylene alkylene group containing from 1 to 10 and preferably from 1 to 6, more preferably from 2 to 4 carbon atoms. A is most preferably an alkylene group having from 2 to 4 carbon atoms.

Most preferably, said statistical copolymer is derived essentially from at least one monomer (b) of the formula (IV):

Thus, the most preferred monomer (b) comprises N-(2-methacryloyloxyethyl)ethyleneurea (2-(2-oxo-1-imidazolidinyl)ethyl 2-methyl-2-propenoate).

In one preferred embodiment of all aspects of the invention, the copolymer is essentially derived from co-monomers (a) and (b) (as defined above) and additionally one or more further co-monomers (c), wherein the or each co-monomer (c) is an ethylenically unsaturated compound different from either (a) or (b) defined above. Such co-polymers may have additional performance features imparted to them by the incorporation therein of such additional co-monomers (c).

Copolymers derived essentially from co-monomers (a) and (b) (as defined above in relation to all aspects) and additionally one or more co-monomers (c) are particularly preferred for imparting the dual properties of dynamic friction increase and viscosity index improvement to the resulting lubricant composition. Preferably, the or each co-monomer (c) in this embodiment is an alkyl acrylate or methacrylate wherein, preferably, the alkyl substituent is a straight chain or branched chain alkyl group, preferably having from 1 to 5 carbon atoms.

The statistical copolymers generally have a molecular weight in the range from 1,000 to 1,000,000 g/mol, preferably in the range from 10×10³ to 500×10³ g/mol and more preferably in the range from 20×10³ to 300×10³ g/mol. The values are based on the weight-average molecular weight of the polydisperse polymers in the composition. This parameter is determined by GPC as measured against the earlier-described standards.

Preferably, said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC as measured against the earlier-described standards within the range of 10,000 to 100,000 g/mol. More preferably, said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC as measured against the earlier-described standards within the range of 10,000 to 60,000 g/mol.

The preferred copolymers which can be obtained by polymerizing unsaturated ester compounds preferably have a polydispersity M_(w)/M_(n) in the range from 1.05 to 4.0. This parameter can also be determined by GPC as measured against the earlier-described standards.

The preparation of the polyalkyl esters from the above-described compositions is known per se. For instance, these polymers can be effected especially by free-radical polymerization, and also related processes; for example controlled radical polymerization processes such as ATRP (Atom Transfer Radical Polymerization) when applied to starting mixtures of co-monomers. Such preparation methods are known in the art.

The polymerization is preferably carried out in a nonpolar solvent. These include hydrocarbon solvents, for example aromatic solvents such as toluene, benzene and xylene, saturated hydrocarbons, for example cyclohexane, heptane, octane, nonane, decane, dodecane, which may also be present in branched form. These solvents may be used individually and as a mixture. Particularly preferred solvents are mineral oils, natural oils and synthetic oils, and also mixtures thereof. Among these, very particular preference is given to mineral oils.

In said statistical copolymers, the monomer units originating from monomer (b) preferably constitute from 1 to 10 weight percent of the total weight of said statistical copolymer. More preferably, the monomer units originating from monomer (b) constitute from 4 to 8 weight percent of the total weight of said statistical copolymer.

Additionally, the monomer units originating from monomer (a) constitute at least 90 weight percent of the total weight of said statistical copolymer. More preferably, the monomer units originating from monomer (a) constitute the remainder of said statistical copolymer.

Most preferably, the monomer units originating from monomer (b) constitute from 1 to 6 weight percent of the total weight of said statistical copolymer, wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC against the earlier-described standards within the range of 40,000 to 60,000 g/mol.

PREPARATIVE EXAMPLES OF COMPONENT I.B

The following examples of component i.b illustrate the preparation of poly(alkyl methacrylates) useful in the invention.

Example B-1

Mass Monomer Mixture Composition C12-C15 Methacrylate 1876.14 g  Ethylene Urea methacrylate 160.00 g Initial Charge Monomer mixture 2036.14 g  Dodecylmercaptan  17.20 g Butyl Acetate 200.00 g Feed tert-Butyl per-2-ethylhexanoate  10.00 g Butyl Acetate 300.00 g Replenishment step tert-Butyl per-2-ethylhexanoate  8.00 g Butyl Acetate  5.40 g Dilution 100N oil 305.40 g

A 5 L reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with the monomer mixture, butyl acetate and dodecylmercaptan (Initial charge). The reaction mixture was inerted under nitrogen for 15 min and heated to 100° C. At 100° C., the polymerization initiator was added over the course of 60 minutes (Feed). The mixture was held at temperature for 60 minutes, after which the replenishment of initiator was added completely (Replenishment step). The mixture was continually held for 60 minutes. Afterwards, the butyl acetate was removed in vacuo, and the product was redissolved in oil to achieve the final product (Dilution).

Example B-2

Mass Monomer Mixture Composition C12-C15 Methacrylate 1500.91 g  Ethylene Urea methacrylate 128.00 g Initial Charge Monomer mixture 1628.91 g  Dodecylmercaptan  24.00 g t-Butyl-dodecylmercaptan  14.40 g Butyl Acetate 160.00 g Feed tert-Butyl per-2-ethylhexanoate  8.00 g Butyl Acetate 240.00 g Replenishment step tert-Butyl per-2-ethylhexanoate  6.40 g Butyl Acetate  4.32 g Dilution 100N oil 736.00 g

A 5 L reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with the monomer mixture, butyl acetate and dodecylmercaptan (Initial charge). The reaction mixture was inerted under nitrogen for 15 min and heated to 100° C. At 100° C., the polymerization initiator was added over the course of 60 minutes (Feed). The mixture was held at temperature for 60 minutes, after which the replenishment of initiator was added completely (Replenishment step). The mixture was continually held for 60 minutes. Afterwards, the butyl acetate was removed in vacuo, and the product was redissolved in oil to achieve the final product (Dilution).

Example B-3

Mass Monomer Mixture Composition C12-C15 Methacrylate 292.99 g Ethylene Urea methacrylate  12.00 g Initial Charge Monomer mixture 304.99 g Dodecylmercaptan  2.58 g Butyl Acetate  30.00 g Feed tert-Butyl per-2-ethylhexanoate  1.50 g Butyl Acetate  45.00 g Replenishment step tert-Butyl per-2-ethylhexanoate  1.20 g Butyl Acetate  0.81 g Dilution 100N oil 144.30 g

A 1 L reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with the monomer mixture, butyl acetate and dodecylmercaptan (Initial charge). The reaction mixture was inerted under nitrogen for 30 min and heated to 100° C. At 100° C., the polymerization initiator was added over the course of 60 minutes (Feed). The mixture was held at temperature for 60 minutes, after which the replenishment of initiator was added completely (Replenishment step). The mixture was continually held for 60 minutes. Afterwards, the butyl acetate was removed in vacuo, and the product was redissolved in oil to achieve the final product (Dilution).

Example B-4

Mass Monomer Mixture Composition C12-C15 Methacrylate 292.99 g  Ethylene Urea methacrylate 12.00 g Initial Charge Monomer mixture 304.99 g  Dodecylmercaptan 4.50 g tert-Butyl-dodecylmercaptan 2.70 g Butyl Acetate 30.00 g  Feed tert-Butyl per-2-ethylhexanoate 1.50 g Butyl Acetate 45.00 g  Replenishment step tert-Butyl per-2-ethylhexanoate 1.20 g Butyl Acetate 0.81 g Dilution 100N oil 138.45 g 

A 1 L reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with the monomer mixture, butyl acetate and 30 min and heated to 100° C. At 100° C., the polymerization initiator was added over the course of 60 minutes (Feed). The mixture was held at temperature for 60 minutes, after which the replenishment of initiator was added completely (Replenishment step). The mixture was continually held for 60 minutes. Afterwards, the butyl acetate was removed in vacuo, and the product was redissolved in oil to achieve the final product (Dilution).

Examples of comparative poly(alkyl methacrylates) not showing the benefits of the invention (as demonstrated in the subsequent performance examples) are as follows.

Comparative Example B-C-1

Mass Monomer Mixture Composition C12-C15 Methacrylate 83.5 g Initial Charge Nexbase 3020 oil 16.50 g Feed Monomer mixture 83.50 g Dodecylmercaptan 1.25 g tert-Butyl-dodecylmercaptan 0.75 g 2,2-Bis(tert-butyl peroxy)butane 0.33 g Replenishment step 3 × 2,2-Bis(tert-butyl peroxy)butane 3 × 0.25 g

A 500 mL reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with Nexbase 3020 oil (Initial charge). The reaction mixture was inerted under nitrogen for 15 min and heated to 140° C. At 140° C., The monomer mixture, dodecylmercaptan, and initiator were added over the course of 3.5 hours (Feed). The mixture was held at temperature for 90 minutes, after which the temperature was lowered to 120° C. and the replenishment of initiator was added at every hour (3 Replenishment steps).

Comparative Example B-C-2

Mass Monomer Mixture Composition C12-C15 Methacrylate 2604.82 g  N,N-dimethylaminopropyl 184.25 g methacrylamide Initial Charge 100N oil 550.00 g Feed Monomer mixture 2789.07 g  Dodecylmercaptan  23.65 g tert-Butyl per-2-ethylhexanoate  13.75 g Replenishment step tert-Butyl per-2-ethylhexanoate  11.00 g 100N oil  7.43 g Dilution 100N oil 660.00 g

A 5 L reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with 100N oil (Initial charge). The reaction mixture was inerted under nitrogen for 15 min and heated to 100° C. At 100° C., The monomer mixture, dodecylmercaptan, and intiator were added over the course of 120 minutes (Feed). The mixture was held at temperature for 30 minutes, after which the replenishment of initiator was added completely (Replenishment step). The mixture was continually held for 60 minutes. Afterwards, the product was further diluted in oil to achieve the final product (Dilution).

Comparative Example B-C-3

Mass Monomer Mixture Composition C12-C15 Methacrylate 3078.43 g  N,N-Dimethylaminopropyl 217.75 g  methacrylamide Initial Charge 100N oil 406.25 g  Feed Monomer mixture 3296.18 g  Dodecylmercaptan 48.75 g tert-Butyl-dodecylmercaptan 29.25 g 2,2-Bis(tert-butyl peroxy)butane 26.00 g Replenishment step 2,2-Bis(tert-butyl peroxy)butane 58.50 g

A 5 L reactor equipped with a reflux condenser, mechanical stirrer, and thermocouple was charged at room temperature with 100N oil (Initial charge). The reaction mixture was inerted under nitrogen for 15 min and heated to 140° C. At 140° C., The monomer mixture, dodecylmercaptan, and initiator were added over the course of 120 minutes (Feed). The mixture was held at temperature for 30 minutes, after which the temperature was lowered to 120° C. and the replenishment of initiator was added completely (Replenishment step). The mixture was continually held for 120 minutes.

The properties of these materials are shown in Table 1 below.

mass of mercaptan chain transfer average functional agents related molecular C12-15MA EUMA DMAPMAAm monomer to monomer weight solids [wt %] [wt %] [wt %] [mol %] mass [%] M_(w) [g/mol] [%] B-1 92 8 0 11 0.8 50,000 87 B-2 92 8 0 11 2.4 20,000 69 B-3 96 4 0 5 0.8 50,000 68 B-4 96 4 0 5 2.4 20,000 69 B-C-1 100 0 0 0 2.4 20,000 84 B-C-2 93 0 7 10 0.9 50,000 68 B-C-3 93 0 7 10 2.5 20,000 88

In a preferred embodiment of the method of the first aspect of the invention, the lubricant composition resulting from step (i) additionally comprises (i.c) an ashless dispersant, wherein said dispersant is present in an amount that is effective in combination with the copolymer (i.b) to increase the dynamic coefficient of friction of the lubricant composition. As the examples illustrate hereafter, the added presence of the dispersant imparts a higher dynamic coefficient of friction to the oil than that obtained through addition of the copolymer alone.

In this preferred aspect of the invention, the monomer units originating from monomer (b) preferably constitute from 6 to 10 weight percent of the total weight of said statistical copolymer, and said statistical copolymer preferably has a weight-average molecular weight, Mw, as measured by GPC against the earlier-described standards within the range of 10,000 to 40,000 g/mol.

Also in this preferred embodiment, the ashless dispersant comprises one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds. Preferably the ashless dispersant consists of one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds derived from polyalkylene polyamines.

Ashless dispersants useful in the practice of the present invention include hydrocarbyl succinimides, hydrocarbyl succinamides, mixed ester/amides of hydrocarbyl-substituted succinic acid, hydroxyesters of hydrocarbyl-substituted succinic acid, and Mannich condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines. Also useful are condensation products of polyamines and hydrocarbyl substituted phenyl acids. Mixtures of these dispersants can also be used.

Basic nitrogen containing ashless dispersants are well known lubricating oil additives, and methods for their preparation are extensively described in the patent literature. For example, hydrocarbyl-substituted succinimides and succinamides and methods for their preparation are described, for example, in U.S. Pat. Nos. 3,018,247; 3,018,250; 3,018,291; 3,361,673 and 4,234,435. Mixed ester-amides of hydrocarbyl-substituted succinic acids are described, for example, in U.S. Pat. Nos. 3,576,743; 4,234,435 and 4,873,009. Mannich dispersants, which are condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines are described, for example, in U.S. Pat. Nos. 3,368,972; 3,413,347; 3,539,633; 3,697,574; 3,725,277; 3,725,480; 3,726,882; 3,798,247; 3,803,039; 3,985,802; 4,231,759 and 4,142,980. Amine dispersants and methods for their production from high molecular weight aliphatic or alicyclic halides and amines are described, for example, in U.S. Pat. Nos. 3,275,554; 3,438,757; 3,454,55 and 3,565,804.

The preferred dispersants are the alkenyl succinimides and succinamides. The succinimide or succinamide dispersants can be formed from amines containing basic nitrogen and additionally one or more hydroxy groups. Usually, the amines are polyamines such as polyalkylene polyamines, hydroxy-substituted polyamines and polyoxyalkylene polyamines. Examples of polyalkylene polyamines include diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine. Low cost poly(ethyleneamines) (PAM's) averaging about 5 to 7 nitrogen atoms per molecule are available commercially under trade names such as “Polyamine H”, “Polyamine 400”, Dow Polyamine E-100″, etc. Hydroxy-substituted amines include N-hydroxyalkyl-alkylene polyamines such as N-(2-hydroxyethyl)ethylene diamine, N-(2-hydroxyethyl)piperazine, and N-hydroxyalkylated alkylene diamines of the type described in U.S. Pat. No. 4,873,009. Polyoxyalkylene polyamines typically include polyoxyethylene and polyoxypropylene diamines and triamines having average molecular weights in the range of 200 to 2500. Products of this type are available under the Jeffamine trademark.

To form the ashless dispersant, the amine is readily reacted with the selected hydrocarbyl-substituted dicarboxylic acid material, e.g., alkylene succinic anhydride, by heating an oil solution containing 5 to 95 wt. % of said hydrocarbyl-substituted dicarboxylic acid material at about 100° to 250° C., preferably 125° to 175° C., generally for 1 to 10 hours (e.g., 2 to 6 hours) until the desired amount of water is removed. The heating is preferably carried out to favor formation of imides or mixtures of imides and amides, rather than amides and salts. Reaction ratios of hydrocarbyl-substituted dicarboxylic acid material to equivalents of amine as well as the other nucleophilic reactants described herein can vary considerably, depending on the reactants and type of bonds formed. Generally from 0.1 to 1.0, preferably from about 0.2 to 0.6 (e.g., 0.4 to 0.6), equivalents of dicarboxylic acid unit content (e.g., substituted succinic anhydride content) is used per reactive equivalent of nucleophilic reactant, e.g., amine. For example, about 0.8 mole of a pentamine (having two primary amino groups and five reactive equivalents of nitrogen per molecule) may preferably be used to convert into a mixture of amides and imides, a composition derived from reaction of polyolefin and maleic anhydride having a functionality of 1.6; i.e., preferably the pentamine is used in an amount sufficient to provide about 0.4 equivalents (that is, 1.6 divided by (0.8×5) equivalents) of succinic anhydride units per reactive nitrogen equivalent of the amine.

Use of alkenyl succinimides which have been treated with a borating agent are also suitable for use in the compositions of this invention as they are much more compatible with elastomeric seals made from such substances as fluoro-elastomers and silicon-containing elastomers. Dispersants may also be post-treated with many reagents known to those skilled in the art (see, for example U.S. Pat. Nos. 3,254,025; 3,502,677 and 4,857,214).

The preferred ashless dispersants are polyisobutenyl succinimides formed from polyisobutenyl succinic anhydride and an alkylene polyamine such as triethylene tetramine or tetraethylene pentamine wherein the polyisobutenyl substituent is derived from polyisobutene having a number average molecular weight in the range of 300 to 3000 (preferably 400 to 2500). It has been found that selecting certain dispersants within the broad range of alkenyl succinimides produces fluids with improved frictional characteristics. The most preferred dispersants of this invention are those wherein the polyisobutene substituent group has a molecular weight of approximately 950 atomic mass units, the basic nitrogen containing moiety is polyamine (PAM).

The ashless dispersants of the invention can be used in any amount that is effective to improve the dynamic coefficient of friction of the lubricant composition when present therein in addition to the above-defined copolymers. However, the ashless dispersants are typically used from about 0.1 to about 10.0 mass % in the finished lubricant, preferably from about 0.5 to about 7.0 mass %, and most preferably from about 2.0 to about 5.0 mass %. The co-operation between the copolymer and the ashless dispersant in increasing friction manifests itself in the achievement of friction increases that are greater than those achieved by the same amount of copolymer when used alone.

Preferably, in the method of first aspect of the invention, the lubricant composition resulting from step (i) additionally comprises one or more performance enhancing additive packages.

The function of the performance additive package is to confer more desirable friction characteristics on the finished lubricants. While the presence of the statistical copolymers s themselves increases the level of friction of the fluid, further refinement of the friction properties the fluids may be useful in modern transmissions. The performance additive packages can further improve the level of high speed friction but also concurrently reduce the levels of low speed friction. The slope of the relationship of the friction coefficient at high speed to that at low speed is referred to as the dμ/dv of the fluid. In modern transmissions utilizing modulated or slipping clutches, it is important to have a positive dμ/dv characteristic, i.e. friction increasing with increasing sliding speed, to prevent stick-slip from occurring in the clutch. Stick-slip in automotive clutches is commonly referred to as shudder and is felt by the operator as a vibration in the vehicle (see for example: R. F. Watts and R. K. Nibert, “Prediction of Low Speed Clutch Shudder in Automatic Transmissions Using the Low Velocity Friction Apparatus”, 7th International Colloquium on Automotive Lubrication, Technische Akademie Esslingen, presented: Ostfildern, Germany, January 1990).

Performance additive packages useful in the present invention are well known to those skilled in the art. They are concentrates consisting of mixtures of additive chemicals such as anti-wear agents, anti-oxidants, friction modifiers, inhibitors, detergents, etc., that when treated at appropriate dosages in lubricating base oils confer desirable properties to the resulting lubricant. In the case of the present invention these additive packages would be those capable of producing automatic transmission fluids (ATFs), continuously variable transmission fluids (CVTFs), dual clutch transmission fluids (DCTFs) and other fluids that are commonly used in conjunction with oil lubricated oil-lubricated clutches. The additive packages suitable for use in this invention would all contain ashless dispersants as described above. Examples of these types of performance additive packages would be: Infineum T4575, Infineum T4904 and Infineum T4300 (available from Infineum, USA, Linden, N.J., USA); Hitec 2038, Hitec 2435 and Hitec 3491 (available from Afton, Inc., Richmond, Va., US); Lubrizol 9680, Lubrizol 6373 and Lubrizol DCT 03 VW (available from the Lubrizol Corporation, Wickliffe, Ohio, USA). These performance additive packages generally treat from about 5.0 to about 20.0 mass percent in the lubricating base fluid mixture.

In the uses of the second and third aspects of the invention, the at least one statistical copolymer is preferably that statistical copolymer defined above, and preferably that statistical copolymer defined in any of claims 2 to 8 inclusive, 10, or 15 to 20 inclusive below.

More particularly, in the use of the third aspect of the invention, it is preferred that the ashless dispersant comprises one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds, and more preferably consists of one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds derived from polyalkylene polyamines.

Preferably, in the uses of the second and third aspects of the invention, said clutch is utilised in a power-transmission device, and said device is a vehicular automatic transmission. Preferably, said automatic transmission is of a type selected from the group consisting of stepped automatic transmissions, automated manual transmissions, continuously variable transmissions and dual clutch transmissions.

The oil-lubricated clutches of the invention are commonly used friction clutches made of alternating steel reaction plates and steel plates coated with a composite material which when sliding relative to each other provide high friction coefficients and act as brakes. The composite coating, or lining, is often based of a cellulosic paper which can then be impregnated with various minerals or particles, such as graphite and diatomaceous earth, to further modify the frictional characteristics and physical strength of the lining. The lining is further coated with, or saturated with, a resin, e.g. phenolic or silicate polymer, to give it mechanical strength and wear resistance. These oil-lubricated clutch components are manufactured for example by BorgWarner Incorporated, Auburn Hills, Mich.; Dynax Corporation, Hokkaido, Japan.

Except in Examples, or where otherwise explicitly stated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, numbers of carbon atoms, and the like are to be understood as modified by the word “about”. Unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain isomers, by-products, derivatives, and other materials which are normally understood to be present in the commercial grade. However, the amount of each chemical component is presented as “active ingredient”, i.e. exclusive of any solvent or diluent oil which may be customarily present in the commercial material, unless otherwise indicated. It is also to be understood that the upper and lower amount, range and ratio limits set forth herein may be independently combined as can ranges of different components. As used herein, the expression “derived essentially from” permits the inclusion of substances which do not materially affect the basic and novel characteristics of the composition under consideration.

Specific features and examples of the invention are presented for convenience only, and other embodiments according to the invention may be formulated that exhibit the benefits of the invention. These alternative embodiments will be recognized by those skilled in the art from the teachings of the specification and are intended to be embraced within the scope of the appended claims.

Performance Example 1

Each of the poly(alkyl methacrylates) of table 1 was dissolved in a Group III mineral oil at 10.0 mass percent (in the diluted form). No other additives were present in the oil, and thus this test illustrates the friction-increasing property of the statistical copolymers of the invention per se.

Measurements of dynamic coefficients of friction versus velocity were made on these solutions at four temperatures (40, 80, 120 and 150° C.) using Borg Warner SD 1777 paper based friction material running against a SAE 1035 tumbled steel reaction plate at an applied load of 1 MPa. Table 2 gives the results of the evaluations, showing friction coefficients recorded at 2.5 m/s for each polymer.

TABLE 2 Friction Coefficient at 2.5 m/s Polymer 40° C. 80° C. 120° C. 150° C. B-C-1 0.124 0.114 0.118 0.124 B-C-2 0.108 0.106 0.110 0.115 B-C-3 0.121 0.115 0.119 0.122 B-1 0.132 0.136 0.142 0.148 B-2 0.135 0.137 0.144 0.149 B-3 0.145 0.146 0.153 0.158 B-4 0.133 0.136 0.139 0.141

It can easily be seen that the comparative materials (B-C-1; B-C-2; B-C-3) gave noticeably lower friction coefficients at each condition than the corresponding products of the invention (B-1; B-2; B-3; B-4). Coefficients approaching 0.160 were achieved with the products of the invention whereas the highest value recorded with the comparative material was 0.124.

In these tests, it is particularly apparent that the presence of the comonomer (b) in the examples of the invention resulted in a significant increase in dynamic coefficient of friction. Comparative example B-C-1 is the ‘control’ test derived simply from the monomer (a) component (mixture of C12-C15 methacrylates). Direct comparison of B-C-1 particularly with examples B-2 and B-4 (all having the same Mw of 20,000 g/mol) shows the impact of monomer (b) on increasing the dynamic coefficient of friction.

Comparison with the results for B-C-2 and B-C-3 shows that, in contrast, the presence of another heteroatom-containing monomer derived from methacrylic acid but not having the structure of monomer (b) (and specifically, not having the required R⁴ substituent) resulted in a lowering of the dynamic coefficient of friction, even as against the control test of B-C-1. Thus, in these statistical copolymers their effect on this aspect of friction is controlled by the nature of the monomer (b).

Likewise, it is apparent from the results for the examples of the invention that B-3 exhibited the optimum performance of the polymers per se, corresponding to the preferred combination of low monomer (b) content (within the range of 1 to 6 percent by weight) and molecular weight within the range of 40,000 to 60,000 g/mol.

Performance Example 2

Solutions of two of the poly(alkyl methacrylates), B-1 and B-2, of the invention from Example 1 were treated with ashless dispersants of the PIBSA-polyamine type. Dispersant A is a PIBSA-Polyamine adduct produced from a polyisobutylene of 2225 molecular weight which is post treated with boric acid. Dispersant B is a PIBSA-Polyamine adduct produced from polyisobutylene of 950 molecular weight. Both ashless dispersants were simply added to the solutions of poly(alkyl methacrylates) at 1.65 mass percent active ingredient.

The friction versus velocity curves of the resulting solutions were measured as above. It can be seen in FIGS. 1 and 2 that in each case high speed friction was increased by addition of the ashless dispersant.

In addition, the relationship between friction coefficient and sliding speed was favourably altered, with the dispersant reducing the drop-off in friction coefficient as the sliding speed increased. The velocity dependence of friction was decreased across the range of sliding speeds measured.

Performance Example 3

In a third experiment seven more finished fluids were made up by treating the poly(alkyl methacrylates) into Group III mineral oil at 10.0 mass percent (diluted form) however in this case each of the lubricant samples also contained 10.0 mass percent of Infineum T4215, an additive package commonly used in automatic transmission fluids (ATFs).

The friction versus velocity measurements were again made as described above. The results of these measurements are given in Table 3 below:

TABLE 3 Friction Coefficient at 2.5 m/s Polymer 40° C. 80° C. 120° C. 150° C. B-C-1 0.155 0.147 0.144 0.147 B-C-2 0.134 0.129 0.127 0.128 B-C-3 0.135 0.128 0.128 0.127 B-1 0.161 0.156 0.152 0.152 B-2 0.167 0.160 0.156 0.156 B-3 0.162 0.154 0.150 0.152 B-4 0.161 0.153 0.148 0.149

The increase in dynamic coefficient of friction seen for the illustrated examples of the invention in Table 2 is also seen in the presence of the performance package. All the exemplified polymer systems B-1 to B-4 inclusive showed an improvement over the control system based on B-C-1. Again, the presence of co-monomer (b) was essential to obtaining the increase in dynamic friction, and the comparative example made from a different co-monomer led to friction reduction, not the desired friction increase.

Further it can be seen by comparing FIGS. 3 and 4 that the presence of the additive system resulted in the fluid having dμ/dV character that is improved over the polymer per se results. Thus, the dμ/dV curve for the simple system of the poly(alkyl methacrylates) per se in oil shows a more negative gradient than for the corresponding examples that included the performance package. 

What is claimed is:
 1. A method of increasing the friction in an oil-lubricated friction clutch having a cellulose-based friction lining, or in a power-transmission device utilising said clutch, the method comprising: (i) preparing or otherwise obtaining a lubricant composition comprising (i.a) a major amount of oil of lubricating viscosity, and (i.b) one or more copolymers of ethylenically unsaturated esters present in an amount effective to increase the dynamic coefficient of friction of the lubricant composition when used in said clutch or device; and (ii) lubricating said clutch or device with the lubricant composition resulting from step (i); wherein at least one copolymer (i.b) is a statistical copolymer derived essentially from the following co-monomers (a) and (b): (a) at least one ethylenically unsaturated ester compound of the formula (I):

in which R is hydrogen or methyl, R¹ is a linear or branched chain alkyl group having from 6 to 36 carbon atoms, and R² and R³ are each independently hydrogen or a group of the formula —COOR′ in which R′ is hydrogen or a linear or branched chain alkyl group having from 6 to 36 carbon atoms; and (b) at least one ethylenically unsaturated ester compound of the formula (II):

in which R is hydrogen or methyl, X is oxygen, sulfur or an amino group of the formula —NH— or —NR^(a)— in which R^(a) is an alkyl radical having from 1 to 40 carbon atoms, R⁴ is a radical comprising from 2 to 100 carbon atoms and contains at least 2 oxygen, sulfur or nitrogen atoms, R⁵ and R⁶ are each independently hydrogen or a group of the formula —COX′R⁷ in which X′ is oxygen or an amino group of the formula —NH— or —NR^(a′)— in which R^(a′) is an alkyl radical having from 1 to 40 carbon atoms, and R⁷ is a radical comprising from 1 to 100 carbon atoms; wherein the co-monomer units originating from co-monomer (b) constitute from 0.1 to 30 weight percent of the total weight of said statistical copolymer.
 2. The method of claim 1, wherein the monomer units originating from co-monomer (b) constitute from 1 to 10 weight percent of the total weight of said statistical copolymer.
 3. The method of claim 2, wherein the co-monomer units originating from co-monomer (b) constitute from 4 to 8 weight percent of the total weight of said statistical copolymer.
 4. The method of claim 2, wherein the co-monomer units originating from monomer (a) constitute at least 90 weight percent of the total weight of said statistical copolymer.
 5. The method of claim 1, wherein the co-monomer units originating from monomer (a) constitute the remainder of said statistical copolymer.
 6. The method of claim 1, wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 10,000 to 100,000 g/mol.
 7. The method of claim 6, wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 10,000 to 60,000 g/mol.
 8. The method of claim 1, wherein the co-monomer units originating from co-monomer (b) constitute from 1 to 6 weight percent of the total weight of said statistical copolymer, and wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 40,000 to 60,000 g/mol.
 9. The method of claim 1, wherein the lubricant composition resulting from step (i) additionally comprises (i.c) an ashless dispersant, wherein said dispersant is present in an amount that is effective in combination with the copolymer (i.b) to increase the dynamic coefficient of friction of the lubricant composition when used in said clutch or device.
 10. The method of claim 9, wherein the co-monomer units originating from co-monomer (b) constitute from 6 to 10 weight percent of the total weight of said statistical copolymer, and wherein said statistical copolymer has a weight-average molecular weight, Mw, as measured by GPC within the range of 10,000 to 40,000 g/mol.
 11. The method of claim 9, wherein the ashless dispersant comprises one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds.
 12. The method of claim 10, wherein the ashless dispersant comprises one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds.
 13. The method of claim 11, wherein the ashless dispersant consists of one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds derived from polyalkylene polyamines.
 14. The method of claim 12, wherein the ashless dispersant consists of one or more alkenyl- or polyalkenyl-substituted succinimide or succinamide compounds derived from polyalkylene polyamines.
 15. The method of claim 1, wherein, in said statistical copolymer, the R⁴ radical in the co-monomer units originating from at least one co-monomer (b) comprises at least one nitrogen atom and at least one oxygen atom.
 16. The method of claim 1, wherein, in said statistical copolymer, the R⁴ radical in the co-monomer units originating from at least one co-monomer (b) comprises at least one urea group.
 17. The method of claim 16, wherein, in said statistical copolymer, the R⁴ radical in the co-monomer units originating from at least one co-monomer (b) is a group of the formula (III)

in which A is a hydrocarbylene connecting group containing from 1 to 50 carbon atoms.
 18. The method of claim 17, wherein said statistical copolymer is derived essentially from at least one co-monomer (b) of the formula (IV):


19. The method of claim 1, wherein said statistical copolymer is derived essentially from at least one co-monomer (a) of the formula (I) wherein the R¹ radical is a straight chain alkyl group having between 12 and 15 carbon atoms.
 20. The method of claim 19, wherein, in said statistical copolymer, the R⁴ radical in the co-monomer units originating from at least one co-monomer (b) is a group of the formula (III)

in which A is a hydrocarbylene connecting group containing from 1 to 50 carbon atoms.
 21. The method of claim 1, wherein said clutch is utilised in a power-transmission device, and said device is a vehicular automatic transmission.
 22. The method of claim 21, wherein said automatic transmission is of a type selected from the group consisting of stepped automatic transmissions, automated manual transmissions, continuously variable transmissions and dual clutch transmissions.
 23. The method of claim 1, wherein the lubricant composition resulting from step (i) additionally comprises one or more performance enhancing additive packages. 